1. Field of the Invention
The present invention relates to a stereoscopic computer graphics (CG) image generating apparatus for making stereoscopic vision possible by stereoscopically displaying two-dimensional images generated from three-dimensional structural information, and also relates to a stereoscopic TV apparatus for displaying a stereoscopic image.
2. Related Art of the Invention
An example of a prior art stereoscopic image generating apparatus is shown in FIG. 10. According to this apparatus, three-dimensional structural information, describing a three-dimensional shape of an object by a surface model, is input (the object is approximated by a plurality of small surfaces called polygons, and the structural information defines the three-dimensional positions of the vertices of each polygon and the faces and edges formed by the polygons), and the object defined by this information is arranged in a world coordinate system. Then, projection transformation sections 1 and 2 calculate the two-dimensional positions of the object that would be projected on a film when photographed by an imaginary camera, and rendering sections 3 and 4 determine the brightness and color (e.g., R, G, B values) of an image within each polygon on the basis of the material of the object, the type of the light source used, and the three-dimensional positions.
For example, a geometric model of a polyhedron, such as the one shown in FIG. 11(a), is described by the three-dimensional coordinates of vertices V1 to V8 and the data structure (forming faces and edges) of the geometric model, as shown in FIG. 11(b), and the object described by this information is arranged in the world coordinate system as shown in FIG. 12(a). Then, an image (vertices) of the object projected on a screen 50, as viewed from viewpoint E of the camera, is calculated. Next, the positions on the screen of the faces and edges formed by the vertices and their brightness and color are calculated to produce an image for output. At this time, in order to produce a stereoscopic image, images as viewed from at least two viewpoints need to be calculated; therefore, camera parameters must be specified as shown in FIG. 12(b), that is, 2Wc which is the spacing between a plurality of cameras, CL and CR which are the positions of the camera viewpoints, P which is the three-dimensional coordinates of the converging point of the cameras, and f which is the focal length of the cameras (or .theta. which is the field of view).
FIG. 18 shows an example of a prior art stereoscopic TV apparatus for displaying a stereoscopic image.
This apparatus comprises two CRTs with crossed polarizing filters attached to their respective display surfaces, and a half-silvered mirror is used to combine the two display images. When viewed by a viewer wearing glasses constructed from corresponding polarizing filters, the images are shown to the viewer's left eye and right eye, respectively.
However, in the above prior art stereoscopic CG generating apparatus, the plurality of camera parameters have to be changed according to the viewing distance and screen size, but in actuality, these parameters are adjusted by a CG operator, based on his experience, by viewing the generated stereoscopic CG images and setting the parameters so that an easy-to-view image can be presented to the viewer. There is therefore the problem that if stereoscopic CG images generated with improperly adjusted parameters are displayed on a stereoscopic image display device, the binocular parallax of the stereoscopic images (expressing, for example, the difference between the horizontal positions of the same vertices in the left and eight images in terms of view angle) often exceeds the allowable range of the viewer, resulting in unnatural stereoscopic images that tend to increase eye strain.
In view of the above problem of the prior art stereoscopic CG image generating apparatus, it is an object of the present invention to provide a stereoscopic image generating apparatus that can automatically generate natural and easy-to-view stereoscopic images for a viewer regardless of the viewing distance and screen size.
In the case of the prior art stereoscopic TV apparatus, when the same stereoscopic image signal is input, if the screen size is different, the binocular parallax of displayed images is also different. FIG. 19 explains this; that is, binocular parallax .DELTA.s on a small display screen (a) increases to .DELTA.L on a large display screen (b). If this binocular parallax becomes too large, the viewer will have difficulty in achieving stereoscopic vision, thus increasing eye strain.
Difficulty in achieving stereoscopic vision means that, if binocular parallax .DELTA.N becomes large, and the distance between the image display screen and point P where the object is perceived for stereoscopic viewing increases, as shown in FIG. 20(a), there arises a conflict between the adjustment of the viewer's eye lenses and the distance perceived by stereoscopic vision, and (if P moves further closer) binocular stereoscopic vision cannot be achieved. In the case of FIG. 20(b), in stereoscopic images an object at distance .infin. is displayed with binocular parallax coinciding with the interpupillary distance of the viewer. If the binocular parallax .DELTA.F becomes larger than that, the viewer will be unable to achieve binocular stereoscopic vision.
For recent computer graphic terminals, multisync monitors are widespread that can be switched between multiple resolution modes. The resolution (display frequency) can be switched over a wide range, for example, from a low resolution mode of 640.times.400-pixel screen generally used for personal computers to a high resolution mode of 2000.times.1000-pixel for workstations. If one multisync display is used to switch between these image signals, the displayed size of an image consisting of the same number of dots varies according to the resolution of the image signal because the display screen size is the same. FIG. 19 shows this; that is, part (c) shows a display of a low-resolution image signal, and part (d) shows a display of a high-resolution image signal. In part (d), the displayed image is small, while in part (c), binocular parallax .DELTA.s is larger than .DELTA.t.
When stereoscopic CG images or the like are displayed on such a display, binocular parallax of displayed images varies greatly according to the image resolution, in some cases making it difficult for the view to achieve stereoscopic vision and thus tending to increase eye strain.
Currently, there are three types of broadcast video signals, HDTV, EDTV, and NTSC. These signal formats differ not only in resolution but also in screen aspect ratio, and hence, there arise differences in display size. Furthermore, in some display methods, the size can be changed as in a windowing environment. Accordingly, binocular parallax of displayed images varies greatly, in some cases making it difficult for the view to achieve stereoscopic vision and tending to increase eye strain.
The present invention is also intended to resolve the above-outlined problems involved in stereoscopic presentation of natural images, and it is also an object of the invention to make it possible to produce easy-to-view, natural-looking stereoscopic images by automatically adjusting the amount of binocular parallax according to the screen (window) size even when the same stereoscopic image signal is input.